Magnetic Polypyrrole-Gelatin-Barium Ferrite Cryogel as an Adsorbent for Chromium (VI) Removal.

Polypyrrole-gelatin aerogels, containing magnetic barium ferrite (BaFe) particles, (PPy-G-BaFe) were synthesized by oxidative cryopolymerization and used as adsorbents for the removal of Cr(VI) from aqueous media. The removal was performed at pH 4, which was shown to be the optimal value, due to HCrO4- being the dominant species in these conditions and its more favorable adsorption and reduction compared to CrO42-, present at pH > 4. It was found that the presence of magnetic BaFe particles had no effect on the adsorption performance of PPy aerogels in terms of capacity and kinetics, which was attributed to its relatively low content in the composite. After the adsorption, the presence of chromium in the composites was confirmed by EDX and its electrostatic interaction with the adsorbent was pointed at by vibrational spectroscopy, corresponding to the accepted adsorption mechanism. The adsorption kinetics followed the pseudo-second-order model pointing at chemisorption being the rate-limiting step. The adsorption isotherm data was best fitting with the Temkin model. The maximum adsorption capacity, calculated using the Langmuir model, was 255.8 mg g-1 (the maximum experimental value was 161.6 mg g-1). Additionally, the possibility of Cr(VI) adsorption in the presence of Cl-, Br-, NO3- and SO42- as interfering ions was shown.

Effect of a Zr-Based Metal-Organic Framework Structure on the Properties of Its Composite with Polyaniline.

Composites of polyaniline (PANI) and Zr-based metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were synthesized by the oxidative polymerization of aniline in the presence of MOF templates with the MOF content in the resulting materials (78.2 and 86.7 wt %, respectively) close to the theoretical value (91.5 wt %). Scanning electron microscopy and transmission electron microscopy showed that the morphology of the composites was set by the morphology of the MOFs, whose structure was mostly preserved after the synthesis, based on the X-ray diffraction data. Vibrational and NMR spectroscopies pointed out that MOFs participate in the protonation of PANI and conducting polymer chains were grafted to amino groups of UiO-66-NH2. Unlike PANI-UiO-66, cyclic voltammograms of PANI-UiO-66-NH2 showed a well-resolved redox peak at around ≈0 V, pointing at the pseudocapacitive behavior. The gravimetric capacitance of PANI-UiO-66-NH2, normalized per mass of the active material, was also found to be higher compared to that of pristine PANI (79.8 and 50.5 F g-1, respectively, at 5 mV s-1). The introduction of MOFs into the composites with PANI significantly improved the cycling stability of the materials over 1000 cycles compared to the pristine conducting polymer, with the residual gravimetric capacitance being ≥100 and 77%, respectively. Thus, the electrochemical performance of the prepared PANI-MOF composites makes them attractive materials for application in energy storage.

Polypyrrole-Barium Ferrite Magnetic Cryogels for Water Purification.

Magnetic polypyrrole-gelatin-barium ferrite (PPy-G-BaFe) cryogels/aerogels were synthesized by one-step oxidative cryopolymerization of pyrrole in the presence of various fractions of barium ferrite (BaFe) nanoparticles, dispersed in aqueous gelatin solution. The successful incorporation of BaFe into the composites was confirmed by elemental analysis and scanning electron microscopy paired with an energy-dispersive X-ray detector. The maximum achieved content of BaFe in the resulting material was 3.9 wt%. The aerogels with incorporated BaFe had significantly higher specific surface area and conductivity, reaching 19.3 m2 g-1 and 4 × 10-4 S cm-1, respectively, compared to PPy-G aerogel, prepared in the absence of BaFe (7.3 m2 g-1 and 1 × 10-5 S cm-1). The model adsorption experiment using an anionic dye, Reactive Black 5, showed that magnetic PPy-G-BaFe aerogel, prepared at 10 wt% BaFe fraction, had significantly higher adsorption rate and higher adsorption capacity, compared to PPy-G (dye removal fraction 99.6% and 89.1%, respectively, after 23 h). Therefore, the prepared PPy-G-BaFe aerogels are attractive adsorbents for water purification due to their enhanced adsorption performance and the possibility of facilitated separation from solution by a magnetic field.

Carbon Materials Derived from Poly(aniline-co-p-phenylenediamine) Cryogels.

Nitrogen-containing carbon derivatives were prepared by the carbonization of poly(aniline-co-p-phenylenediamine) cryogels in inert atmosphere. Lower aniline fraction in the comonomer mixture used for preparation of the cryogels led to the decrease of their thermal stability, a consequent increase of carbonization degree, and less defective structure of carbonized materials. The resulting carbonaceous products had up to 4 orders of magnitude higher specific surface area than their respective cryogel precursors, the highest value 931 m2 g-1 being achieved for carbonized poly(p-phenylenediamine) cryogel. Electrochemical characterization of the carbon derivatives demonstrated that the decrease in aniline concentration during the synthesis of the precursor cryogels led to higher gravimetric capacitance for corresponding carbonized materials. These materials can potentially be used for energy storage applications.